This proposal is to investigate a laser-assisted, thermomechanical process for cladding of high melting refractory metals on low melting substrates without melting or damaging the underlying substrates. This unique process fuses the clad material to the substrate without gross melting of the clad layer and substrate. Careful control of laser parameters is required to produce proper thermal coupling for metallurgical bonding (fusion) of the clad layer with the substrate material without thermally damaging or melting the substrate. An analytical thermal model will be employed to establish the necessary laser parameter requirements. In the proposed process, refractory metal foils will be metallurgically bonded to steel substrates by bringing the foil into thermal contact with the substrate alloy and using a scanning laser beam to heat the foil and substrate to the alloy eutectic temperature. When the interface between the foil and substrate reaches this temperature, a eutectic liquid will form which will subsequently resolidify after passage of the scanning laser beam and form a metallurgical bond between the foil and substrate material. Spring-loaded rollers will be used to hold the foil in place and a protective gas shroud will be employed to prevent oxidation of the clad layer during the laser treatment. Post cladding treatments consisting of carburizing and oxidizing furnace treatments will be investigated to demonstrate the ability to produce refractory metal carbides and oxides on the clad surface, which should have application where high temperature oxidation and wear resistance is required. The post cladding treatment is necessary because currently it is not possible to clad ceramics by direct fusion with a laser. In this Phase I research the plan is to produce clads of a variety of refractory metals on ferrous substrates under laser parameters established by the thermal model, perform tests to evaluate the integrity of the bond, perform post cladding carburizing and oxidation treatments and evaluate the oxidation behavior and wear resistance of these surfaces, and compare the results to those of a conventional fusion-cladding process. A Phase II is planned which will investigate specific applications of interest to potential Phase III sponsors. If the research is successful, Phase III will investigate commercialization of this process. This process has the potential to produce clads of high melting refractory metal alloys, carbides and oxides on low melting point substrates without significant melting or thermal damage to the underlying substrate material. The proposed process provides for cladding of large surface areas at twice the coverage rate of conventional fusion-cladding processes. The process has potential for use in conventional industrial and advanced aerospace applications, such as advanced turbine components, rocket nozzles, high temperature combustion systems, and chemical process industry systems.
